Heat transfer device employing fins in a fluid stream

ABSTRACT

The heat exchanger comprises a device coupled in heat exchanging relation with a fluid stream by means of an arcuate array of radially directed, circumferentially spaced, thermally conductive fins with the mean plane of each fin being generally parallel of the axis of revolution of the arcuate array. The fins are corrugated into a wave-like geometry, with the waves increasing in amplitude with increase in radial distance from the axis of revolution, and with the wave fronts running generally laterally to the axis of revolution of the array. The fluid stream flows between adjacent fins in a serpentine path through the array in the axial direction.

United States Patent Lavering May 6,1975

[ HEAT TRANSFER DEVICE EMPLOYING FINS IN A FLUID STREAM [75] Inventor: Gordon R. Lavering, Belmont, Calif.

[73] Assignee: Varian Associates, Palo Alto, Calif.

[22] Filed: Nov. 12, 1973 [21] Appl. No.: 415,068

[52] US. Cl. 165/80; 165/183; 165/180;

[51] Int. Cl F281 7/00 [58] Field of Search 165/74, 80, 183; 315/538 [56] References Cited UNITED STATES PATENTS 2,289,984 7/1942 Mouromtseff et a1 165/80 X 2,347,957 5/1944 McCullough 165/183 X 2,535,721 12/1950 Chausson 165/80 X FOREIGN PATENTS OR APPLICATIONS 874,395 8/1961 United Kingdom 165/183 Primary Examiner-Charles J. Myhre Assistant Examiner-T. W. Streule, Jr.

Attorney, Agent, or FirmStanley Z. Cole; Leon F. Herbert; John J. Morrissey [57] ABSTRACT The heat exchanger comprises a device coupled in heat exchanging relation with a fluid stream by means of an arcuate array of radially directed, circumferentially spaced, thermally conductive fins with the mean plane of each fin being generally parallel of the axis of revolution of the arcuate array. The fins are corrugated into a wave-like geometry, with the waves increasing in amplitude with increase in radial distance from the axis of revolution, and with the wave fronts running generally laterally to the axis of revolution of the array. The fluid stream flows between adjacent fins in a serpentine path through the array in the axial direction.

6 Claims, 5 Drawing Figures PPJENTED HAY 6|975 2| FIG-.5 PRIOR ART HEAT TRANSFER DEVICE EMPLOYING FINS IN A FLUID STREAM BACKGROUND OF THE INVENTION The present invention relates in general to heat exchanging apparatus, and more particularly to an im' proved heat exchanger particularly suited for cooling anode structures of electron beam tubes, wherein a stream of fluid coolant such as air is directed through a circular array of cooling fins for removing heat from the anode of the tube.

DESCRIPTION OF THE PRIOR ART Heretofore, heat exchangers have been proposed for cooling the anodes of electron beam tubes. In one such prior art device, a circular array of radially directed cooling fins was coupled to the anode with the fins projecting outwardly therefrom in circumferentially spaced relation from each other to accomodate an axial flow of fluid through the array for cooling of the fins and the anode. In addition, the fins were corrugated into a wave-like geometry with the wave fronts being generally parallel to the axis of revolution of the circular array of fins. Such an arrangement of cooling fins is disclosed and claimed in US Pat. No. 3,293,480, patented Dec. 20, 1966 and assigned to the same assignee as the present invention.

While the aforedescribed prior art fin geometry provided improved heat transfer. as contrasted with noncorrugated cooling fins, it is desirable to provide a further increase in heat transfer efficiency.

It has also been proposed in the prior art to punch out of the wave shaped fins bridge-like tabs which project from the planes of the individual fins into the region between adjacent fins for improving the heat transfer from the fins to the cooling air stream, particularly near the outer periphery of the radially divergent fins where a relatively large percentage of the air flow is not in intimate contact with the cooling fins. This type of geometry, employing the punched out bridge-shaped tabs, which are referred to in the art as louvers, has resulted in improved heat transfer efficiency as contrasted with the heat transfer performance of corrugated fins for which the wave fronts of the waves run parallel to the longitudinal axis of the array and to the fluid flow path.

It has also been proposed in the aforecited patent to cause the fins to curve in a clockwise or anti-clockwise direction around the axis of revolution of the array to describe involute of a circle curves such that the circumferentiated spacing between adjacent fins is maintained over the radial extent of the fins. This tends to provide a more efficient utilization of the air flow passage between adjacent fins, particularly at the outer periphery of the array. However, the performance of the involute array is approximately the same as the per formance of the louvered array.

The louvered fins have certain definite problems. One of the problems is that the flow of air, or other fluid, past the bridge-like tabs provides a source of noise which is particularly shrill in the audio-range of 600 Hz to L200 Hz. In addition, the louvers collect lint which impedes the flow of fluid coolant through the array and which results in a loss of heat transfer effi' ciency.

SUMMARY OF THE PRESENT INVENTION The principal object of the present invention is to provide an improved heat transfer device employing fins in a fluid coolant stream.

In one feature of the present invention, the heat transfer device includes a circular array of heat exchanging fins which are corrugated to provide a wavelike geometry, with the wave fronts being disposed at a substantial angle to the direction of air flow through the array of fins, such air flow being parallel to the axis of revolution of the array, whereby improved heat transfer is achieved.

In another feature of the present invention. the corrugations in the circular array of fins define wave geometries wherein the wave fronts are at a substantial angle to the axis of revolution and to the fluid flow stream, and wherein the amplitude of the wave-like corrugations increases in a radially outward direction, thereby increasing the length of the fluid flow path as a function of radius and causing some of the stream to be directed toward the center or core, of the fin array for improved heat transfer.

In another feature of the present invention, the wave crests in the adjacent fins of the array are in registration to define therebetween a serpentine fluid flow path axially of the array, such flow path being of generally uni form thickness at a given radius from the center of the array.

Other features and advantages of the present invention will become apparent upon a perusal of the follow ing specifications taken in connection with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary side elevational view, partly broken away, of the anode of an electron beam tube employing an array of cooling fins of the present invention,

FIG. 2 is an enlarged schematic line diagram of a ser pentine shaped flow path defined between adjacent fins of the array of FIG. 1,

FIG. 3 is a view similar to that of FIG. 2 depicting an alternative wave shape,

FIG. 4 is a plan view of a prior art louvered cooling fin, and

FIG. 5 is a sectional view through the louvered fin structure of FIG. 4 depicting the flow path between two adjacent fins.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, there is shown an electron beam collector or anode assembly 11 of an electron beam tube such as a power grid tube, klystron, travelling wave tube, or the like, wherein an electron beam is collected on the interior surfaces of a cylindrical evacuated collector bucket 12, as of copper, having an outer cylindrical shape. A circular array of cooling fins 13 is coupled or affixed to the outer cylindrical periphery of the collector 12, as by brazing or soldering. The fins 13 in a typical example are fitted within longitudinal recesses 14 in the periphery of the collector bucket 12 and are brazed at their root portions to the interior walls of the recesses 14.

The cooling fins 13 are thin sheets ofa thermally conductive material, such as copper or aluminum and preferably copper, which radiate outwardly from the collector bucket 12 in a circular array. In a typical example, the fins 13 are made of a copper sheet 0.025 inches thick having a radial extent of approximately 3.25 inches. The fins 13 are corrugated to form a wave-like geometry, with the wave fronts, as defined by the ridge lines 15, running along the crest of the wave and ex tending at an angle to and generally laterally of the axis of revolution of the circular array of fins. In addition, the amplitude of the waves increases in the radial outward direction from the axis of revolution to define a serpentine-shaped fluid flow path 16 between adjacent wavy fins as more clearly shown in FIG. 2.

A fluid coolant stream, as of air, is directed generally longitudinally of the axis of revolution of the array through the adjacent serpentine-shaped flow paths 16 between adjacent fins 13. A cylindrical baffle 17, as of copper, surrounds the periphery of the circular array of fins for confining the flow of fluid coolant to the serpentine path 16 between the adjacent fins 13. Suitable manifolds, not shown, serve to direct the fluid coolant through the fins l3 and to collect the fluid coolant for exhaust after passage through the fin array.

In a typical example, the circumferential spacing between adjacent fins is approximately equal to the amplitude of the wavelike distortion of the fins. The mean plane of each fin 13, as indicated by the broken line 18, is parallel to the axis of revolution of the array. In addition, the wave-like corrugations of each fin 13 need not be of the half-wave type as shown in FIGS. 1 and 2 but may be of a more sinusoidal shape with substantially equal corrugation of the fin on the opposite sides of the mean plane 18 of each fins. Equal wave amplitudes on opposite sides of the fin are shown in FIG. 3 where the corrugations are more of a triangular wave-shape than of the sinusoidal form shown in FIGS. 1 and 2.

In operation, the length of the serpentine flow path 16 increases with increase in radius from the axis of revolution of the array. Increasing the flow path length tends to increase the local impedance of the coolant passage to fluid flow and to counteract the reduction in impedance due to the increase in width of the flow path near the outer perimeter of the array. The serpentine shape of the flow path 16 causes the molecules of the fluid in the stream to impinge and to scrub the surfaces of he fins 13 as shown by the arrows in FIG. 2. It is believed that this contributes substantially to increased heat transfer between the fluid stream and the fins for improved heat transfer efficiency. Moreover, it is believed that the corrugations which have increased amplitude near the outer periphery tend to direct some of the flow toward the center core 12 and toward the root portions of the cooling fins 13 for improved heat transfer efficiency.

It is also believed that at the confluence of the inwardly directed stream flow and the axially directed flow stream near the inner core there is produced a vortexing action which tends to further scrub the surfaces of the fins 13 for improved heat transfer.

Referring now to FIGS. 4 and 5, there is shown the prior art louvered fin 21 having the pushed out bridgeshaped tabs or louvers 22 located near the outer periphery of the fin 21. The problem with this type of fin geometry is that heat transfer to the bridge-shaped louver portions 22 is restricted clue to the break in the continuity of the fin caused by the bridge 22 being severed along opposite edges from the fin at 23, such that the heat flow into the bridge portion 22 is only from opposite ends thereof. Thus, although the louvered fin geometry provides additional heat transfer area in the central region of the fluid flow stream, the apparent heat transfer advantage of the louvered portion is not fully obtained due to the relatively poor heat flow to the louver portion 22. Moreover, because the fin is perforated in forming the louvers 22, the flow of air through the array of fins in the axial direction generates substantial noise. More particularly, in one of the typical prior art louvered geometries, there is a peak in the noise power spectrum in the audio frequency range between 600 Hz and 1,200 Hz. This turns out to be a rather shrill sound resulting in substantial discomfort to nearby workmen and operators.

The advantage of the corrugated fins of the present invention is that they provide a substantial increase in heat transfer efficiency. More particularly, the heat transfer horsepower parameter, i.e., a quantity proportional to the product of fluid flow rate in cubic feet per minute times pressure drop in the fluid flow stream required to maintain the core 12 at a given temperature, is directly related to the amount of horsepower required to move the fluid coolant through the cooling array. In one case, this parameter was reduced by percent utilizing the corrugated fins of the present invention as contrasted with a comparable louvered fin geometry as shown in FIGS. 4 and 5. Moreover, the corrugated fin geometry of the present invention provides a relatively clean aerodynamic flow passage 16 through the array, thereby eliminating the objectionable shrill noises previously produced by the louvered fin geometries. Also, the relatively clean aerodynamic surfaces of the present invention prevent the collection of lint in a fin array. Furthermore, due to the increased heat transfer efficiency of the corrugated fins of the present invention, the amount of fin material, such as copper, can be reduced by a factor of at least 20 percent resulting in substantial cost savings. In addition, the fluid ducting or manifolds required for directing the fluid coolant through the fin array can be reduced in diameter, and the fans and blowers can be reduced in weight and size. These latter advantages are particularly suited for airborne applications.

Although the wavy fins 13 of the present invention have, thus far, been described as being radially directed to provide a fluid flow path thickness that increases with increase in radial distance from the core 12, this is not a requirement. In particular, the radial fins 13 may be curved into an involute of a circle arc such that the spacing between adjacent fins is constant over the radial extent of the fins.

Also, the crest of the waves in the fins 13 need not be continuous but may be interrupted. However, the interruptions in adjacent waves in a given fin 13 should be staggered so as to minimize non-serpentine shaped portions of the fluid flow paths 16.

While there have been described and illustrated several specific embodiments of the invention, it will be clear that variations in the details of the embodiments specifically illustrated and described may be made without departing from the true spirit and scope of the invention as defined in the appended claims and their legal equivalents.

What is claimed is:

1. In a heat transfer apparatus for transferring heat between a device and a stream of fluid wherein said device comprises an elongate member and a sleeve surrounding said elongate member and where said stream of fluid flows between said elongate member and said nearer to said axis of revolution of said array. surrounding sleeve member 2. The apparatus of claim 1 wherein said elongate an arcuate array of circumferentially-spaced member is a beam collector structure of an electron thermally-Conductive fins Coupled in heat" tube, said fins being cooling fins for transfer of heat exchanging relationship with Said elongate member 5 from said collector to said fluid stream, and wherein and P outwardly therefrom; each of Said the amplitude of said wave-like configuration is subfins bemg corrugated F' configufa' stantially zero at the innermost radial extent of each of tion, the mean plane of the wave-like configuration Said fins of each of Said fins being generally parallel to the 3. The apparatus of claim 2 wherein said fins are axis of revolution of said arcuate array;

made of copper sheets of generally uniform thickness.

4. The apparatus of claim 1 wherein the wave crests of said wave-like configuration in adjacent ones of said fins are in registration with each other such that the spacing between adjacent fins at a given radius from the axis of revolution of the array is substantially uniform for all the fins in the array.

5. The apparatus of claim 1 wherein said fins are imthe wave amplitude of said wave-like configuration increasing with increase in radial distance along said mean plane outward from said axis of revolution of said array;

the wave fronts of said wave-like configuration for each of said fins running generally laterally of said axis of revolution of said array to accommodate the flow of coolant fluid along serpentine paths between adjacent ones of said fins parallel to said axis perforateof revolution so that coolant fluid flowing between The apparatus f laim 2. h r said fins are adjacent fins in proximity to the outer perimeter of mad r m aluminum heets Of generally uniform said array of fins traverses a flow path which is thickness. longer than the flow path for coolant fluid flowing 

1. In a heat transfer apparatus for transferring heat between a device and a stream of fluid wherein said device comprises an elongate member and a sleeve surrounding said elongate member and where said stream of fluid flows between said elongate member and said surrounding sleeve member an arcuate array of circumferentially-spaced thermallyconductive fins coupled in heat-exchanging relationship with said elongate member and extending outwardly therefrom, each of said fins being corrugated into a wave-like configuration, the mean plane of the wave-like configuration of each of said fins being generally parallel to the axis of revolution of said arcuate array; the wave amplitude of said wave-like configuration increasing with increase in radial distance along said mean plane outward from said axis of revolution of said array; the wave fronts of said wave-like configuration for each of said fins running generally laterally of said axis of revolution of said array to accommodate the flow of coolant fluid along serpentine paths between adjacent ones of said fins parallel to said axis of revolution so that coolant fluid flowing between adjacent fins in proximity to the outer perimeter of said array of fins traverses a flow path which is longer than the flow path for coolant fluid flowing nearer to said axis of revolution of said array.
 2. The apparatus of claim 1 wherein said elongate member is a beam collector structure of an electron tube, said fins being cooling fins for transfer of heat from said collector to said fluid stream, and wherein the amplitude of said wave-like configuration is substantially zero at the innermost radial extent of each of said fins.
 3. The apparatus of claim 2 wherein said fins are made of copper sheets of generally uniform thickness.
 4. The apparatus of claim 1 wherein the wave crests of said wave-like configuration in adjacent ones of said fins are in registration with each other such that the spacing between adjacent fins at a given radius from the axis of revolution of the array is substantially uniform for all the fins in the array.
 5. The apparatus of claim 1 wherein said fins are imperforate.
 6. The apparatus of claim 2, wherein said fins are made from aluminum sheets of generally uniform thickness. 